The present application relates generally to seals having improved flexibility for reducing leakage, and more particularly to shim seals for reducing leakage between adjacent stationary components of turbomachinery.
Leakage of hot combustion gases and/or cooling flows between turbomachinery components generally causes reduced power output and lower efficiency. For example, the hot combustion gases may be contained within a turbine by providing pressurized compressor air around the hot gas path. Typically, leakage of the high pressure cooling flows between adjacent stator components (such as shrouds, nozzles, and diaphragms) into the hot gas path may lead to detrimental parasitic losses. Such parasitic losses may reduce efficiency and require an increase in burn temperature, and thereby an increase in NOx (CO produced at low temperature, only occurs at part load) and a decrease in engine gas turbine efficiency to maintain a desired power level as compared to an environment void of such stator-stator leakage. Turbine efficiency thus can be improved by reducing or eliminating stator-stator leakage locations.
Preventing leakage between stator-stator component junctions with seals is complicated by the fact that adjacent stator components have surfaces of different shapes and may expand differently under high temperature conditions causing misalignment between the components. Further, the seals must pass manufacturing, assembly and installation limitations, meet robustness constraints associated with turbomachinery, and withstand the relatively high forces and temperatures produced in turbomachinery.
Currently, turbomachinery typically employ woven metallic cloth based seals, including impervious outer shims, positioned between adjacent stator components to limit the leakage of cooling flows therebetween. Such cloth seals often have a porous woven wire mesh cloth layer wrapped around a metal shim with a curved “shepherds hook” on either side. Manufacturing variations, however, involved in creating the “shepherds hook” and in assembling the cloth/metal seals may result in seals that do not adequately reduce or substantially eliminate the leakage rate between adjacent turbomachinery components, such as a stator-stator junctions. Similarly, some cloth seals may tend to become crimped or otherwise plastically deformed within the space or gap between components during installation or assembly, and thereby perform less effectively than desired.
Accordingly, it would be desirable to reduce or substantially eliminate leakage between turbomachinery components, such as between adjacent stator components, and more particularly between misaligned turbomachinery components by utilizing flexible seals. Therefore it is desirable to provide for an improved seal assembly for use between stator components and other components in a heavy duty gas turbine engine, that are sufficiently flexible so as to provide adequate sealing during use and in the presence of any misalignment between the components. It is further desirable that such seals be substantially temperature resistant and wear resistant (i.e., long component life) and meet the manufacturing, assembly, installation and robustness requirements associated with turbomachinery.